We explain what electrical conductivity is and based on what it varies. Electrical conduction of metals, water and soil.
What is electrical conductivity?
Electrical conductivity is the capacity of the matter to allow the flow of electric current through their particles. This capacity depends directly on the atomic and molecular structure of the material, as well as other physical factors such as the temperature to which it is or the state it is in (liquid, solid, gaseous).
Electrical conductivity is the opposite of resistivity, that is, the resistance to the passage of electricity of the materials. There are then good materials and bad electrical conductive materials, insofar as they are more or less resistant.
The symbol to represent conductivity is the Greek letter sigma (σ) and its unit of measurement is the siemens per meter (S / m) or 𝛀-1⋅ m-1. For its calculation, the notions of electric field (E) and conduction current density (J), as follows:
J = σE, from where: σ = J / E
The conductivity varies depending on the state of matter. In liquid media, for example, it will depend on the presence of dissolved salts in them that generate ions positively or negatively charged, and are the electrolytes responsible for conducting electric current when the liquid is subjected to an electric field.
On the other hand, solids have a much more closed atomic structure and with less movement, so the conductivity will depend on the cloud of electrons shared by the bands of Valencia and the conduction band, which varies according to the atomic nature of matter: the metals are good electrical conductors and no metals, on the other hand, good resistors (or insulators, such as plastic).
Water conductivity
The Water in general, it is a good electrical conductor. However, this capacity depends on its margin of Total Dissolved Solids (TDS), since the presence of salts and minerals in the water forms the electrolytic ions that allow the passage of electric current. Proof of this is that distilled water, which are eliminated (using distillation and other methods) all ions dissolved in it, and it does not conduct electricity.
In this way, the conductivity of salt water is greater than that of fresh water. The increase in the conductivity rate can be recorded as dissolved ions are added to the liquid, until reaching a limit of ionic concentration in which pairs of ions are formed, positive with negative, which cancel their charge and prevent conductivity. increase more.
Soil conductivity
The soilsIn general, they have different electrical conductivity, depending on various factors such as water irrigation or the amount of salts they present. As in the case of water, more saline soils will be better electrical conductors than less saline ones, and this distinction is often determined by the amount of water they receive (since water can "wash" salts from the soil).
This level of salinity is often confused with the sodicity of the soil (the presence of sodium), when in reality salinity refers to the abundance of the cations of sodium (Na +), potassium (K +), calcium (Ca2 +) and magnesium (Mg2 +), together with the cations of chlorine (Cl–), sulfate (SO42-), bicarbonate (HCO3–) and carbonate (CO32-).
Thus, in many cases techniques such as washing (for very saline soils) or the injection of other neutralizing elements (such as sulfur) are used for very basic ones. This can often be determined by electrical conduction tests.
Metal conductivity
Metals are generally excellent electrical conductors. This is because atoms of this type of material are combined by formation of metal links. In metals, electrons stay around the metal like a cloud, moving around tightly bound atomic nuclei, and it is they that allow electrical flow.
When metal is applied to an electric field, electrons flow freely from one end of the metal to the other, just as it does with the metal. heat, of which they are both good transmitters. That is why the copper and other metals in power lines and electronic devices. The following figure schematically represents the flow of electrons (in red) when an electric field is applied to a metal: